This invention relates to ink jet printing and particularly to preventing leakage of ink from a gap between a traversing orifice band and an ink source.
The invention is embodied in an orifice band ink jet printer wherein the orifice band moves at a constant speed through a stationary source of liquid ink under pressure to sweep modulated columns of ink drops across an advancing sheet of ordinary paper. Ink jets emerging from orifices in the orifice band project between a row of signal responsive charging electrodes where the jets break into drops of uniform size. Drops forming between charging electrodes having a voltage applied thereto retain a charge and are deflected by a constant electrostatic field into an elongated collector for reuse. Drops forming between charging electrodes at a null voltage are uncharged and travel undeflected to deposit on paper as dots of ink. Basic ink jet printers wherein uniform drops forming from a jet are selectively charged for deflection by a constant electrostatic field are described in the following publications:
Sweet, R. G., "High Frequency Oscillography with Electrostatically Deflected Ink Jets", AD 437,951, National Technical Information Service 1964, and "I.B.M. Journal of Research and Development", Vol. 21, No. 1, pages 1-96, January 1977.
A linear array of orifices in a thin plate to form periodically disturbed jets is described for stationary orifices by Cha et al. in U.S. Pat. No. 4,138,689.
Basic features of the orifice band printer are disclosed by the applicant in U.S. Pat. Nos. 3,971,040, 3,972,053, and 4,117,518.
A general feature of orifice band ink jet printers is a desirable distribution of motions consisting of a high frequency modulation of the ink drops, a rapid and constant linear motion of the orifice band, and an unrolling at a moderate speed of paper into a flat configuration for convenient printing, cutting, and assembly into a package comprising a plurality of pages. General features of the traversing orifice band over stationary orifice plates include: reduction of aerodynamic distortions which may occur as drops travel through wakes of preceeding drops; a reduction of standing waves and induced noise on the orifices due to an absence of mechanical contact with the orifice band; and, feasibility of larger charging electrodes which operate on a moderate number of orifices for improved reliability. Features of a traversing orifice band printer having particular application for facsimile publishing include: deposition of uncharged drops for reduced electrostatic distortion; a uniform and closely spaced dot interval with overlap capability to saturate dark areas; and, use of the same orifice band for simultaneous printing of both sides of the paper.
A separation between the orifice band and the stationary ink source provides the advantages just cited but it also results in a leakage of ink through the separation gap. The cited U.S. Pat. No. 3,971,010 describes an orifice band printer wherein the ink which has leaked from the gap and air which has leaked from the air bearing are collected and the ink is reused. The air bearing also functions as an ink seal with air compressed therein preventing entry of the ink so that the ink does not escape beyond its removal channel and port. But the pumping of large amounts of ink through the gap and its conditioning to remove dissolved air is complex and energy inefficient. Further, the air bearing assembly could be made less complex if its function as an ink seal was not required.
It is an object of the invention to substantially stop flow of ink through the separation gap between the orifice band and stationary surface of the ink source assembly.